Conventional seed planters include soil-opener mechanisms for forming furrows in the soil. Such furrows can be formed by a pair of planar disks independently rotatably mounted on the seed planter in a manner so as to cause these disks to penetrate the soil and co-act to form a single furrow as the planter moves across the ground. In a typical arrangement, the disks are mounted on the implement in a skewed manner, one disk skewed relative to the other disk, such that the disks together take on a V-shape to form a single furrow. The "point" of the "V" is disposed forward of the disk centers relative to the disk direction of travel. Further, one disk (the so-called "leading" disk) is typically spaced 1/2 to 1 inch ahead of the other disk (the so-called "trailing" disk) relative to their direction of travel and respective disk centers. Both disks are typically disposed the same depth into the ground. Planting is typically performed with the seed-planter implement traveling through a field at a speed of about three miles per hour (MPH). Each disk is typically 14 inches in diameter and is thus caused to rotate about seventy-two revolutions per minute (RPM).
Preferably, the disks are gapped by as much as 3.2 millimeters at the "point" of the "V" to avoid one disk contacting the other. However, as the disks engage the soil they are caused to deflect and contact each other. Because the circumferential disk portions which contact at the "point" of the "V" move relative to each other, the trailing disk will wear a 1-inch wide annular groove into the leading disk, the groove being spaced about 1/2 inch from the leading disk circumference. Such wear may be so severe that the leading disk must be replaced daily. This, of course, involves undesired cost and can result in excessive non-productive activity.
Affixing hard-facing material and/or applying hard-facing coatings at the disk-wear area are currently not economically practical.
A process for heat-treating agricultural-implement metal disks so as to obtain a metal disk having a hardened surface-area portion is disclosed in U.S. Pat. No. 4,305,272 to Johnson. The method disclosed and claimed as invention in the Johnson patent, however, is entirely different from the present invention discussed hereinbelow. Briefly, the Johnson disks are tempered after being quenched (i.e. cooled), whereas the disks of the present invention are rapidly cooled, and not tempered thereafter. Also, because the '272 Johnson disk is a soil-tilling disk, and has a generally non-planar shape in cross section, slight warpage of the Johnson disk is acceptable. The disk of the present invention is planar; and thus warpage is generally not acceptable. The method of the present invention, unlike the Johnson method, particularly points out and teaches how to avoid disk warpage, therefore. Finally, the Johnson method teaches a method for producing a disk having a central portion and an annular peripheral portion having greater hardness than the central portion. The present invention, on the other hand, teaches and claims methods for producing a disk having a central portion, an annular peripheral edge portion of hardness equal to the central portion, and a second annular portion spaced between the central portion and the peripheral edge portion and having a hardness substantially greater than the disk central and peripheral portions. That is, Johnson teaches hardening a disk edge, whereas the present invention teaches hardening a disk surface portion that is spaced radially inwardly of the disk edge.